Production of water-free nitrocellulose and explosive substances that have a spheroidal shape

ABSTRACT

The invention relates to a method for producing shaped explosive substances, in particular for a propellant charge substrate such as spheroidal propellant charge powder, for example, from a stabilized explosive substance, whereby the stabilized explosive substance is first dissolved in a solvent, the stabilizing substance is then removed from the mixture, and particles are shaped from the resulting mixture. The invention further relates to a method for producing a varnish made from a substantially water-free explosive substance.

The invention relates to a method for producing shaped nitrocellulose as well as explosive substances and propellants according to the preamble of claim 1, to a method for producing a varnish made from a substantially water-free explosive substance, or a varnish made from an explosive substance having a defined water content, according to the preamble of claim 8, to use of a varnish made from a water-free explosive substance according to the preamble of claim 10, and to a varnish made from nitrocellulose according to the preamble of claim 11.

Within the scope of this invention, the term “explosive substances” is understood to mean explosive and/or potentially explosive, in particular solid, liquid, and gelatinous, substances and substance mixtures that are used as explosive agents, propellants, detonating agents, or pyrotechnic devices, or for the manufacture of same.

Explosive substances are used for numerous applications, particularly in the munitions sector. For efficient and effective use, as a rule it is necessary for the explosive substances to be present in a specific geometry, for example in a spherical shape. This allows explosive substances, in the form of propellant charges, for example, to be loaded into shell casings. To ensure homogeneous and uniform combustion of the explosive substances, it is necessary that the explosive substances have a defined structure and defined geometry, the latter being achievable, for example, when the explosive substances are present in uniform sizes, preferably as spherical or spheroidal particles. Nitrocellulose as well as the previously described explosive substances may also represent a raw material for varnish production. Spherical nitrocellulose as raw material for varnish production offers the advantages that in this form it is stabilized, even without moistening agents, is easy to handle, and allows for the incorporation of additives.

One application in the area of explosive substances is the production of spheroidal propellant charge powder. Heretofore, shaping was accomplished by dissolving water-moistened nitrocellulose in ethyl acetate and then distributing this organic phase in an aqueous phase by intensive stirring. In this procedure, basically particles with very irregular sizes are formed. In addition, after being formed the particles are very susceptible to enlargement by coalescence, since the varnish for this type of particle formation must have only a very low viscosity, which in turn facilitates coalescence. After particle formation the solvent is evaporated with stirring, and the nitrocellulose remains in the aqueous phase in the form of rounded particles.

These particles may be separated from the aqueous phase by filtration, for example. In this procedure it is disadvantageous that the resulting spheroidal particles have a very broad particle distribution. In some cases, the proportion of the size range usable for an application is only ⅓ of the total mass, and must be separated by costly screening procedures.

Another method for producing spherical nitrocellulose particles uses an underwater granulator for formation of the particles. The organic phase is pressed through a perforated disk into the aqueous phase, and the strands exiting the orifices in the perforated disk are broken up into particles by a rotating blade on the exit side. It is necessary to screen the formed particles in this method as well. Further disadvantages of this method are that the organic phase for use in the underwater granulator must have such a high consistency that the cylindrical particles which primarily result in the normal stirring process are no longer round. They must therefore be conveyed through long pipes having small cross sections, thereby imparting roundness by the intensive contact with the pipe walls.

High throughputs in the device require high rotational speeds for the blade. The increasing speed of the rotating blade also increases the hydraulic shear forces, which very quickly result in diminished quality due to further uncontrolled size reduction of the particles. The rotational speed of the cutting blade, which is thereby greatly limited from above, significantly restricts the efficiency of the device.

The particles are hardened by stripping the solvent, as in the previously described method.

As a result of the manufacturing process, the particles produced by both methods contain undefined quantities of dispersed water which create an undefined porosity in the finished particle. However, this is a key quality feature for the product, since the porosity greatly influences the combustion of the product. Depending on the use, minimal to high porosities may be desirable, which however must have a precisely defined consistency. For this reason, in the past the water content has been adjusted by dewatering prior to hardening of the particles. This was generally achieved by making use of the osmotic effect created by the addition of sodium sulfate to the aqueous dispersion. The extent of dewatering was controlled by the salt concentration, the length of the reaction, and the temperature. This dewatering process is very difficult to control and produces unsatisfactory results.

An additional disadvantage is that salt residues necessarily remain, at least on the particles, which requires washing steps in the process. Remaining salt residues may inhibit the effectiveness of the explosive substance.

Furthermore, in particular the quantity of sodium sulfate required for water removal entails considerable adverse environmental impacts.

Thus, with the current methods it has not been possible thus far to produce in a simple and economical manner particles made from explosive substances, in particular from nitrocellulose, having a spherical geometry with a uniform size, which have a defined porosity and are substantially pore-, water-, and salt-free.

The object of the invention, therefore, is to provide a method and a substance for producing shaped explosive substances by which the aforementioned disadvantages, in particular porosity, water and salt content, non-uniform particle size, and environmental impacts, are avoided.

This object is achieved by a method according to claims 1 through 8, by use of a varnish made from an explosive substance according to claim 10, and by a varnish made from nitrocellulose/explosive substance according to claim 11.

The method for producing shaped explosive substances, in particular propellant charge powder such as spheroidal propellant charge powder, for example, from an explosive substance stabilized in particular with water comprises the following steps according to the invention:

-   -   Dissolving the stabilized explosive substance in a solvent;     -   Removing the stabilizing substance, in particular water, from         the mixture;     -   Shaping the explosive substance particles; and     -   Collecting the explosive substance particles.

A significant feature of the invention lies in the fact that removal of the stabilizing substance, in particular water, from the mixture allows the explosive substance particles to be shaped without the risk of including a stabilizing substance. As used here, “stabilizing substance” is understood to mean for example water, or also a salt or other organic or inorganic non-reactive or inert substances such as alcohol or softeners, for example.

According to one preferred embodiment of the invention, the stabilizing substance, in particular water, is removed by azeotropic distillation. Thus, in particular with the assistance of pervaporation/steam permeation, the water may be removed from the explosive substance efficiently, effectively, and safely.

According to a refinement of the invention, during and/or after the distillation the solvent is returned to the explosive substance. In this manner it is possible to produce a varnish made from explosive substance having a predefined viscosity, the viscosity being adjustable by the type and/or quantity of solvent as well as by the use of auxiliary agents. Surface-active substances, wetting agents, or separating agents, for example, may be used as auxiliary agents.

If the stabilizing substance is a solid, salt, or other substance difficult to distill, the invention provides that this substance is extracted with suitable solvents. According to the invention a solid phase extraction or precipitation, for example, is also possible if this is compatible with the type of explosive substance, in particular the density and solubility thereof. Extraction by sublimation is also possible, provided that this can be performed safely.

According to a further embodiment of the invention, the shaping of nitrocellulose and/or explosive substance particles is carried out or initiated by jet cutting, in which a jet, preferably a full jet, of an explosive substance-solvent mixture or an explosive substance-solvent solution, in particular a varnish made from an explosive substance, is subdivided by use of a separating device into jet segments having a defined and/or adjustable length which fall into a fluid, preferably a fluid in motion, in which the explosive substance-solvent mixture, in particular varnish made from an explosive substance, is poorly soluble and/or essentially insoluble.

This method is extremely well suited for producing spheroidal particles of approximately equal particle size for processing explosive substance-solvent mixtures.

In the production of the spheroidal particles, the organic phase of the fluid to be processed and from which the particles are to be produced is pressed in the form of a full jet at high velocity from a nozzle. Directly below the nozzle is a rotating cutting tool, composed of short wires which are preferably held in a mounting and point outward, which breaks up the fluid jet into cylindrical segments. As these segments continue to fall, as a result of the surface tension of the fluid they form spherical particles which are collected in a solvent, in particular water.

The size of the particles produced is adjustable as a function of the nozzle diameter, the volumetric flow through the nozzle, the number of cutting wires, and the rotational speed of the cutting tool, and according to the invention lies in the range of 0.1 mm to 10 mm, preferably in the range of 0.2 mm to 2 mm, and particularly preferably in the range of 0.5 mm to 1.5 mm.

One of the significant advantages of the invention is that the jet cutting ensures that it is possible to produce only particles which have a desired size and are adjustable using the aforementioned parameters, and that the explosive substance particles produced essentially contain only explosive substance and solvent, but none, or a precisely defined quantity, of a stabilizing substance. The advantages of the jet cutting method are described below.

The inclination of the cutting plane with respect to the jet axis enables substantially cylindrical particles, which are already approximately spherical, to be cut from the moving jet.

In addition, the cutting device operates in air, thereby permitting very high cutting frequencies and therefore high throughputs.

In contrast to the underwater granulator, the cutting tool does not make contact with the exit orifice.

In addition, the design for carrying out the jet cutting method is simple and economical.

By making use of the advantages of the jet cutting method and employing appropriately matched parameters, losses due to a non-homogeneous particle distribution may be reduced to less than 3%, in particular to less than 2%, of the explosive substance-solvent mixture used.

An explosive substance which is sufficiently viscous and is capable of being handled safely without solvent may be used directly in the jet cutting method.

A further significant advantage of the invention is that explosive substance particles having a defined porosity can be produced, the rate of porosity being adjustable by, for example, introduction of suitable substances, in particular water, into the varnish made from an explosive substance. To this end, substances are preferably used which can be diffused or dissolved out of the explosive substance particle, thereby leaving a cavity in the explosive substance particle. In addition, it is possible to introduce salts or similarly non-reactive substances which remain in solid form in the explosive substance particle.

As the result of such non-explosive residues and/or cavities or pores in the explosive substance particles, the speed and temperature of combustion, and thus the speed of detonation of the explosive substance, may be advantageously influenced.

Similarly, it is also possible to produce multilayer explosive substance particles, whereby in the jet cutting process various varnishes made from an explosive substance may be introduced through one central nozzle and one or more annular nozzles. It is thus possible to produce, for example, an explosive substance having an inwardly increasing speed of combustion, whereby for this purpose an outer layer contains, for example, an appropriate quantity of a stabilizing substance or a slow-combusting explosive substance.

According to a refinement of the present invention, water-containing nitrocellulose is used as stabilizing [sic; stabilized]¹ explosive substance and ethyl acetate is used as solvent. This explosive substance-solvent system is extremely well suited for producing spherical, water- and salt-free nitrocellulose particles which in particular are optimally suited for producing spheroidal propellant charge powder. Translator's Notes: ¹ Substantiated by terminology in claim 7 and amended claim 7.

The object of the invention is further achieved by a method for producing a varnish made from a substantially water-free explosive substance, or a varnish made from an explosive substance having a defined water content, in particular nitrocellulose varnish, from an explosive substance stabilized in particular with water, whereby the method comprises the following steps:

Dissolving the stabilizing [sic; stabilized]² explosive substance in a solvent;

-   -   Removing the stabilizing substance, in particular water, from         the mixture by azeotropic distillation while establishing a         defined water content; and     -   Establishing a predetermined viscosity for the varnish made from         an explosive substance.         ² Substantiated by terminology in claim 8 and amended claim 8.

The significant advantage of this aspect of the invention is based on the fact that a varnish made from a substantially water-free explosive substance is suitable for producing water-free and also salt-free explosive substance particles, since according to the method, before being used for the varnish made from an explosive substance these particles have been removed from a matrix from which the particles were produced.

According to a refinement of the invention, for establishing a predefined viscosity the solvent is returned to the explosive substance before and/or after the distillation. According to the invention, for adjusting the viscosity auxiliary agents, such as in particular surface-active substances, wetting agents, separating agents, and agents for adjusting the viscosity, may be used.

By the use of wetting and/or separating agents it is possible, for example, to optimally match the varnish made from an explosive substance with the materials with which the varnish is combined in the production process, so that, for example, contamination resulting from adhesion of the explosive substance to the equipment used is minimized or completely eliminated. On account of the inherent energy content of an explosive substance, such measures contribute to handling and operational safety in the production of explosive substances.

The object is further achieved by use of a varnish made from a substantially water-free explosive substance, in particular a nitrocellulose varnish, for producing shaped, in particular spherical or spheroidal, explosive substances.

The object of the invention is further achieved by a nitrocellulose varnish composed of at least nitrocellulose and a solvent, the nitrocellulose varnish being substantially water-free.

According to the invention, the nitrocellulose varnish has a viscosity which allows, in particular by use of the jet cutting method, particles having a predefinable particle size in the range of 0.1 mm to 10 mm, preferably in the range of 0.2 mm to 2 mm, and particularly preferably in the range of 0.5 mm to 1.0 mm, to be shaped.

In this manner it is possible to produce a particularly preferred particle size.

As already mentioned above, the nitrocellulose varnish preferably contains auxiliary agents, in particular surface-active substances, wetting agents or separating agents, and agents for adjusting the viscosity.

According to a refinement of the invention, the nitrocellulose varnish is substantially salt-free.

Further embodiments of the invention result from the subclaims. The invention is explained in greater detail below with reference to the embodiments.

EXAMPLE 1

One kilogram nitrocellulose (cellulose nitrate with a N content of approximately 12.5%) which also contained 700 grams nitrocellulose and approximately 300 grams water was dissolved in one liter ethyl acetate, the water fraction being partially dissolved and partially dispersed. The mixture was azeotropically distilled, the azeotrope removed by distillation being dewatered and the ethyl acetate being continuously returned to the distillation. After the water had been completely removed from the nitrocellulose-ethyl acetate solution, this solution was supplied to a jet cutting method, using separating wires with a thickness of 0.05 mm. The resulting particles were collected in water; the water, which may contain a separating agent, was kept in motion by a stirrer. After the complete charge of nitrocellulose had passed through the jet cutting process, the water-particle mixture was concentrated under simultaneous application of a vacuum until the particles were essentially solvent-free in the water. Due to the hydrophobicity of the particles, there is no risk of diffusion of water into the particles. After the distillative concentration the resulting particles were filtered from the particle-water mixture. The particle size obtained was 0.8 mm diameter. The yield relative to the nitrocellulose used was 98.5%.

EXAMPLE 2

One kilogram nitrocellulose (cellulose nitrate with a N content of approximately 13.2%) which also contained 700 grams nitrocellulose and approximately 300 grams water was dissolved in one liter ethyl acetate, the water fraction being partially dissolved and partially dispersed. The mixture was azeotropically distilled, the azeotrope removed by distillation being dewatered and the ethyl acetate being continuously returned to the distillation. After the water had been completely removed from the nitrocellulose-ethyl acetate solution, 100 g metriol trinitrate dissolved in 200 g ethyl acetate was added to the mixture. The resulting varnish made from explosive substance was then supplied to the jet cutting process and further processed, as previously described.

EXAMPLE 3

One kilogram nitrocellulose (cellulose nitrate with a N content of approximately 12.2%) which also contained 700 grams nitrocellulose and approximately 300 grams water was dissolved in one liter ethyl acetate, the water fraction being partially dissolved and partially dispersed. The mixture was azeotropically distilled, the azeotrope removed by distillation being dewatered and the ethyl acetate being continuously returned to the distillation. After the water had been completely removed from the nitrocellulose-ethyl acetate solution, 20 g dibutyl phthalate dissolved in 200 g ethyl acetate was added to the mixture. The resulting nitrocellulose varnish was then supplied to the jet cutting process and further processed, as previously described. It should be noted here that all the sections described above, singly or in any combination, are claimed as essential to the invention. Those skilled in the art are familiar with modifications thereto. 

1. Method for producing shaped nitrocellulose as explosive substances and propellants, in particular propellant charge substrate such as spheroidal propellant charge powder, for example, from an explosive substance stabilized in particular with water, characterized by the following steps: Dissolving the stabilized explosive substance in a solvent; Removing the stabilizing substance, in particular water, from the mixture; Shaping and hardening explosive substance particles, the shaping of the explosive substance particles being carried out or initiated by jet cutting, in which a jet of an explosive substance-solvent mixture or an explosive substance-solvent solution, in particular a varnish made from an explosive substance, is subdivided by use of a separating device into jet segments having a defined and/or adjustable length which fall into a fluid, preferably a fluid in motion, in which the varnish made from an explosive substance is poorly soluble and/or essentially insoluble; and Collecting the explosive substance particles.
 2. Method according to claim 1, characterized in that the stabilizing substance is removed by azeotropic distillation.
 3. Method according to claim 2, characterized in that for producing a varnish made from an explosive substance having a predefined viscosity, the solvent is returned to the explosive substance during and/or after the distillation.
 4. Method according to claim 1, characterized in that the explosive substance particles are hardened after the jet cutting by stripping the solvent, preferably by applying a vacuum.
 5. Method according to claim 1, characterized in that explosive substance particles having a defined porosity are produced, the degree of porosity being adjusted by stabilizing substances, in particular water, introduced and/or remaining in the varnish made from an explosive substance.
 6. Method according to claim 1, characterized in that explosive substance particles having a defined particle size are produced in the range of 0.1 mm to 10 mm, preferably in the range of 0.2 mm to 2 mm, and particularly preferably in the range of 0.5 mm to 1.0 mm.
 7. Method according to claim 1, characterized in that water-containing nitrocellulose is used as stabilized explosive substance and ethyl acetate is used as solvent.
 8. Method for producing a varnish made from an explosive substance having a defined water content, in particular nitrocellulose varnish, for producing shaped explosive substance particles from an explosive substance stabilized in particular with water, the stabilized explosive substance being dissolved in a solvent and the stabilizing substance being removed by azeotropic distillation, characterized in that A defined water content is established in the varnish made from an explosive substance; and For establishing a predefined viscosity the solvent is returned to the explosive substance during and/or after the distillation.
 9. Use of a varnish made from an explosive substance having a defined water content, in particular nitrocellulose varnish, which is substantially free of stabilizing substances for producing shaped, in particular spherical or spheroidal, explosive substances by jet cutting.
 10. Nitrocellulose varnish for producing explosive substances, composed of at least substantially water-free nitrocellulose and a solvent, characterized in that the nitrocellulose varnish is and remains salt-free, and has a viscosity which allows, in particular by use of the jet cutting method, particles having a predefinable particle size in the range of 0.1 mm to 10 mm, preferably in the range of 0.2 mm to 2 mm, and particularly preferably in the range of 0.5 mm to 1.0 mm, to be formed.
 11. Nitrocellulose varnish according to claim 10, characterized in that the nitrocellulose varnish contains auxiliary agents, in particular surface-active substances, wetting agents or separating agents, and agents for adjusting the viscosity. 12-15. (cancelled)
 16. Method according to claim 2, characterized in that the explosive substance particles are hardened after the jet cutting by stripping the solvent, preferably by applying a vacuum.
 17. Method according to claim 2, characterized in that explosive substance particles having a defined porosity are produced, the degree of porosity being adjusted by stabilizing substances, in particular water, introduced and/or remaining in the varnish made from an explosive substance.
 18. Method according to claim 4, characterized in that explosive substance particles having a defined porosity are produced, the degree of porosity being adjusted by stabilizing substances, in particular water, introduced and/or remaining in the varnish made from an explosive substance.
 19. Method according to claim 2, characterized in that explosive substance particles having a defined particle size are produced in the range of 0.1 mm to 10 mm, preferably in the range of 0.2 mm to 2 mm, and particularly preferably in the range of 0.5 mm to 1.0 mm.
 20. Method according to claim 4, characterized in that explosive substance particles having a defined particle size are produced in the range of 0.1 mm to 10 mm, preferably in the range of 0.2 mm to 2 mm, and particularly preferably in the range of 0.5 mm to 1.0 mm.
 21. Method according to claim 5, characterized in that explosive substance particles having a defined particle size are produced in the range of 0.1 mm to 10 nun, preferably in the range of 0.2 mm to 2 mm, and particularly preferably in the range of 0.5 mm to 1.0 mm.
 22. Method according to claim 2, characterized in that water-containing nitrocellulose is used as stabilized explosive substance and ethyl acetate is used as solvent.
 23. Method according to claim 4, characterized in that water-containing nitrocellulose is used as stabilized explosive substance and ethyl acetate is used as solvent.
 24. Method according to claim 6, characterized in that water-containing nitrocellulose is used as stabilized explosive substance and ethyl acetate is used as solvent. 